An important component of disposable absorbent articles such as diapers is an absorbent core structure comprising water-absorbing polymeric particles, typically hydrogel-forming water-swellable polymers, also referred to as absorbent gelling material, AGM, or super-absorbent polymers, or SAP's. This polymer material ensures that large amounts of bodily fluids, e.g. urine, can be absorbed by the article during its use and locked away, thus providing low rewet and good skin dryness.
Water-absorbing polymers are known. For such materials, names such as “highly swellable polymer” “hydrogel” (often also used for the dry form), “hydrogel-forming polymer”, “superabsorbent polymer”, “superabsorbent”, “absorbent gel-forming material”, “swellable resin”, “water-absorbing resin” or the like are also common. These polymers are crosslinked hydrophilic polymers, especially polymers formed from (co)polymerized hydrophilic monomers, graft (co)polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose ethers or starch ethers, crosslinked carboxymethylcellulose, partly crosslinked polyalkylene oxide or natural products swellable in aqueous liquids, for example guar derivatives, water-absorbing polymers based on partly neutralized acrylic acid being the most widespread. The essential properties of water-absorbing polymers are their ability to absorb several times their own weight of aqueous liquids and not to release the liquid again, even under a certain pressure. The water-absorbing polymer, which is used in the form of a dry powder, is converted to a gel when it absorbs liquid and correspondingly to a hydrogel when it absorbs water, as is customary. By far the most important field of use of water-absorbing polymers is the absorption of body fluids. Water-absorbing polymers are used, for example, in diapers for infants, incontinence products for adults or feminine hygiene products. Other fields of use are, for example, those as water-retaining agents in market gardening, as a water store for protection from fire, for liquid absorption in food packaging or quite generally for absorption of moisture.
While many treatments of these materials are known, it has been found that these treatments do not lead to surface-modified polymers having the desired absorption properties. Furthermore, there is a need to deliver a process having a good space-time yield.